Optical waveguide couplers require critical alignment between the fibers being coupled to avoid excessive loss of signal in the coupler. The alignment that is important is that between the cores of the respective fibers, not the exterior circumference of the fiber. If the fiber cladding is slightly off center, or the surface of the fiber is slightly damaged, alignment of the cores is difficult. Even with perfect fiber geometry, alignment of single mode fibers, in which the core diameter is typically of the order of 5 microns, is difficult.
A wide variety of fiber couplers and coupling tools have been proposed, some of which have built-in means for actively aligning the fibers while the connection or coupling is effected. One of these is described and claimed in U.S. Pat. No. 4,217,032 issued Aug. 12, 1980 to Sang K. Sheem. The device described by Sheem is provided with means for raising and lowering one fiber with respect to another as these fibers are retained in a grooved unitary support. A tapered alignment member is fitted into a groove extending perpendicular to one of the fibers and height of that fiber is adjusted by moving the tapered alignment member. While this scheme has been used successfully to adjust the alignment of fibers during coupling, it has the disadvantage of adjusting the fiber in only one of the two planes that are critical in positioning one fiber core with respect to another. The other important adjustment is the lateral position of the fiber. The third degree of freedom, i.e. the spacing between the fibers is slightly less critical than the vertical and lateral positions.